Image processing apparatus and image processing method

Abstract

To resolve or at least reduce trouble related to mismatch between a dynamic range of an HDR video signal and peak luminance of a display. Provided is an image processing apparatus including: a transformation unit configured to transform image signals based on a signal scheme of fixedly handling a display luminance level of reference white into display signals by executing gamma transformation so that the display luminance level of the reference white is maintained using a parameter decided on a basis of a peak luminance level of a display.

The invention claimed is: 
     
       1. An image processing apparatus, comprising:
 a central processing unit (CPU) configured to:
 transform image signals into display signals based on gamma transformation of the image signals, wherein
 a value of a display luminance level of a reference white is constant based on a first parameter, 
 the first parameter is based on a peak luminance level of a display element, 
 the image signals are based on a hybrid log gamma (HLG) scheme that includes a fixedly handling process of the display luminance level of the reference white, 
 the HLG scheme is based on a combination of
 a gamma curve at a luminance level lower than the display luminance level of the reference white, and 
 a logarithmic curve at a luminance level higher than the display luminance level of the reference white. 
 
 
 
 
     
     
       2. The image processing apparatus according to  claim 1 , wherein
 the image signals are normalized at the display luminance level of the reference white, and 
 the gamma transformation on the image signals is based on a first gamma value. 
 
     
     
       3. The image processing apparatus according to  claim 2 , wherein the CPU is further configured to determine the first gamma value such that a maximum luminance level of the display signals is in alignment with the peak luminance level of the display element. 
     
     
       4. The image processing apparatus according to  claim 1 , wherein
 the image signals are normalized at the display luminance level of the reference white, and 
 the CPU is further configured to:
 execute linear transformation on the image signals based on a gain value, 
 determine a second gamma value to restore the display luminance level of the reference white to an original luminance level of the reference white, and 
 execute the gamma transformation on the image signals subjected to the linear transformation, wherein 
 the gamma transformation is executed on the image signals based on the second gamma value. 
 
 
     
     
       5. The image processing apparatus according to  claim 4 , wherein the CPU is further configured to determine the gain value such that a maximum luminance level of the display signals is in alignment with the peak luminance level of the display element. 
     
     
       6. The image processing apparatus according to  claim 4 , wherein
 a value of a maximum luminance level of the display signals is constant based on the second gamma value. 
 
     
     
       7. The image processing apparatus according to  claim 4 , wherein
 the CPU is further configured to execute the linear transformation and the gamma transformation, and 
 the execution of the gamma transformation on the image signals is further based on the second gamma value and system gamma value. 
 
     
     
       8. The image processing apparatus according to  claim 1 , wherein
 the CPU is further configured to select one of a first operation mode or a second operation mode for the transformation of the image signals, and 
 in the first operation mode, the value of the display luminance level of the reference white is constant. 
 
     
     
       9. The image processing apparatus according to  claim 8 , wherein the CPU is further configured to select one of the first operation mode or the second operation mode based on one of a type of the HLG scheme, a user setting, an attribute of the display element, or an environment of the display element. 
     
     
       10. The image processing apparatus according to  claim 8 , wherein the CPU is further configured to:
 determine a gain value such that a maximum luminance level of the display signals is in alignment with the peak luminance level of the display element; and 
 execute linear transformation on the image signals based on the selection of the second operation mode and the gain value. 
 
     
     
       11. The image processing apparatus according to  claim 8 , wherein the CPU is further configured to transform the image signals into the display signals in conformity with ITU-R BT.1886 based on the selection of the second operation mode. 
     
     
       12. The image processing apparatus according to  claim 1 , wherein
 the CPU is further configured to select one of a first transformation or a second transformation, 
 the first transformation corresponds to the gamma transformation on the image signals such that the value of the display luminance level of the reference white is constant, 
 the second transformation corresponds to a linear transformation on the image signals based on a gain value and the gamma transformation on the image signals subjected to the linear transformation, 
 in the second transformation, the CPU is further configured to determine a gamma value to restore the display luminance level of the reference white to an original luminance level of the reference white, and 
 the gamma transformation is executed on the image signals based on the gamma value. 
 
     
     
       13. The image processing apparatus according to  claim 1 , wherein
 the image signals are decoded from an encoded stream, 
 the encoded stream is encoded in conformity with a high efficiency video coding (HEVC) scheme, 
 the HLG scheme for the image signals is further based on a second parameter, and 
 supplemental enhancement information (SEI) associated with the encoded stream includes the second parameter. 
 
     
     
       14. The image processing apparatus according to  claim 13 , wherein the CPU is further configured to:
 align a maximum luminance level of content of a complementary stream with the display luminance level of the reference white, 
 the complementary stream includes at least one of subtitle information or graphics information, and 
 the at least one of the subtitle information or the graphics information is associated with the encoded stream. 
 
     
     
       15. The image processing apparatus according to  claim 1 , wherein
 the image signals include an encoded stream, 
 the encoded stream is encoded in conformity with a high efficiency video coding (HEVC) scheme, 
 the HLG scheme for the image signals is further based on a third parameter, and 
 video usability information (VUI) associated with the encoded stream includes the third parameter. 
 
     
     
       16. A method, comprising:
 transforming image signals into display signals based on gamma transformation of the image signals, wherein
 a value of a display luminance level of a reference white is constant based on a first parameter, 
 the first parameter is based on a peak luminance level of a display element, 
 the image signals are based on a hybrid log gamma (HLG) scheme that includes a fixedly handling process of the display luminance level of the reference white, 
 the HLG scheme is based on a combination of
 a gamma curve at a luminance level lower than the display luminance level of the reference white, and 
 a logarithmic curve at a luminance level higher than the display luminance level of the reference white.